UN peacekeeper health and risk factors --- a systematic scoping review

Background Conflicts, natural disasters, and complex emergencies present substantial health challenges to United Nations (UN) peacekeepers deployed in mission areas. This scoping review aims at summarizing previous research on the health of UN peacekeepers and identifies issues for further investigation. Methods Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for Scoping Reviews, we systematically searched Web of Science, PubMed, EMBASE, Scopus and China National Knowledge Infrastructure (CNKI) for English and Chinese literature published from April 1997 to November 2023. A data charting form was developed by two reviewers to extract relevant themes and provided narrative descriptions. Results We screened 1079 de-duplicated records and included 143 studies in this scoping review. There were 112 studies on the health status of UN peacekeepers, with more than half on mental health problems such as stress and anxiety. Many studies explored the health status of UN peacekeepers in African countries deployed from mainly U.S., Canada, U.K., China, Australia and Norway. There were 39 studies on the health risk factors of UN peacekeepers, including natural environmental, social environmental, psychological, behavioral lifestyle, biological factors and health service factors. There were 62 articles on the health protection of UN peacekeepers, mainly based on previous deployment experience, with a lack of theoretical guidance from global health perspectives. This scoping review found that health problems of UN peacekeepers are complicated, and whose impacts are cross-border. Social environmental factors were explored the most among health risk factors. Disease prevention measures, medical and health measures, and psychosocial measures were the main health protection for UN peacekeepers. Conclusions This scoping review highlighted that health problems of UN peacekeepers were typical global health issues with complicated and cross-border health risk factors. Therefore, comprehensive strategies could be taken from global health perspectives, including multi-phases (before-deployment, during-deployment, and post-deployment), multi-disciplines (public health, medicine, politics, health diplomacy, and others), and multi-levels (the UN, host countries, troop-contributing countries, the UN peacekeeping team, and UN peacekeepers). Supplementary Information The online version contains supplementary material available at 10.1186/s41256-024-00351-4.


Introduction
Since the World War II, the promotion of peace and stability has been a key priority outlined in the Charter of the United Nations (UN), calling for collective action from the international community [1].The first UN peacekeeping mission was established in May 1948, when the UN Security Council authorized the deployment of military observers to the Middle East.Over the past 70 years, more than 1 million peacekeepers have served in over 70 UN peacekeeping operations [2,3].At present, over 100,000 military, police, and civilian personnel from 125 countries serve in 14 active peacekeeping operations.For example, in response to the crisis in South Sudan, the Security Council reinforced the United Nations Mission in South Sudan and reprioritized its mandate towards the protection of civilians, the delivery of humanitarian aid, as well as the implementation of the Cessation of Hostilities Agreement [4].UN peacekeeping has been recognized as a unique and dynamic instrument for assisting conflict-affected countries to achieve lasting peace.
Since 1988, more than 4100 UN peacekeepers have sacrificed their lives in missions, of which more than half occurring in the current peacekeeping missions [1].Between 2000 and 2017, 2042 peacekeepers lost their lives, of which 879 peacekeepers died because of diseases (43.0%), surpassing those because of incidents (29.5%) and violence (19.9%) [3].UN peacekeepers face complex health risk factors, including poor environmental sanitation, imbalanced diet, limited social network, and unhealthy behaviors such as alcohol and drug abuse.Previous research has mentioned that UN peacekeepers had the frequent occurrence of mental health problems such as anxiety and depression, and the high incidence of infectious diseases such as malaria and Acquired Immune Deficiency Syndrome (AIDS), as well as other conditions such as skin diseases and insomnia [5].UN peacekeepers have also been associated with the disease transmission to broader population, such as the cholera outbreak in Haiti in 2010 and the transmission of Human Immunodeficiency Virus (HIV) during and after deployment [6].The UN has previously adopted resolutions emphasizing the health protection of UN peacekeepers and broader population they engage with, such as their families and colleagues [7].For instance, Resolution 1308 (2000) recognized the need to incorporate HIV/ AIDS prevention awareness and skills training for UN peacekeepers, and Resolution 2668 (2022) stressed the importance of mental health and psychosocial support for both UN peacekeepers and people they interact with [8,9].Moreover, the UN has provided peacekeepers with the Core Pre-deployment Training Materials on health knowledge, such as personal hygiene measures and disease prevention guidelines [10].
To the best of our knowledge, there is no comprehensive scoping review on collecting peer-reviewed literature on the health of peacekeepers.Therefore, the aim of this review is to map the existing literature on the health problems, risk factors, and protective measures of UN peacekeepers, whilst identifying the health of UN peacekeepers is a typical global health issue and strategies should be taken from global health perspectives to protect their health.

Search strategy
This scoping review adhered to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) extension for Scoping Reviews [11].The framework proposed by Arksey and O'Malley [12] was used to map the literature pertaining to our research topic.This scoping review identified eligible studies published from April 1997 to November 2023 on health status of UN peacekeepers, health risk factors of UN peacekeepers and health protection of UN peacekeepers.Four major databases including Scopus, PubMed, EMBASE and China National Knowledge Infrastructure (CNKI) were searched.We used a mixture index terms and free text to maximize the retrieval of potentially relevant studies.The terms of "peacekeeper", "health", "disease", "infection", "prevalence", "risk factor", "protection", "prevention", "measure", "control", "policy" and "strategy" were used as keywords and text words to search (see Additional file 1).Reference lists of identified manuscripts were hand-searched.

Inclusion and exclusion criteria
The inclusion criteria included: 1. Type of studies: cross-sectional studies, case-control studies, cohort studies, retrospective studies, longitudinal studies, and medical records report.2. Research subjects: UN peacekeepers.

Outcome variables:
(i) Health status of UN peacekeepers: mental health problems, infectious diseases, and other health problems; (ii) Health risk factors of UN peacekeepers: natural environmental factors, social environmental factors, psychological factors, behavioral lifestyle factors, biological factors, and health service factors; (iii) Health protection of UN peacekeepers: disease prevention measures, medical and health measures, psychological measures, and diplomatic measures.
The exclusion criteria were: (1) articles not specifically related to the health of UN peacekeepers; (2) articles with no research design (opinion pieces, blogs, reviews, news articles, conference paper and gray literature); (3) articles without full texts; If there were multiple reports of the same study, only the article with a full report was included.

Study selection
Two reviewers identified studies using the inclusion and exclusion criteria.Each reviewer screened the titles and abstracts of identified studies independently to preliminarily assess their eligibility according to the inclusion/ exclusion criteria.All reviewers made the decision to include/exclude a study by discussion and consensus where there were disagreements regarding the eligibility of studies.Each of the selected full-text papers was read thoroughly, several times by two reviewers to capture all relevant information and to ensure that nothing important was missed.

Data extraction
Two reviewers independently read the full texts of all initially selected manuscripts and finally included eligible articles according to the inclusion/exclusion criteria.Differences were resolved by discussion and consensus among reviewers.We established an Excel form with a reference number assigned for each included article, and then extracted following data from each study: health status, health risk factors, health protection, author/year, WHO regions: troop-contributing countries, host countries, study designs, and main outcomes.Each extracted data was classified and summarized on outcome variables, and was recorded in the Excel form.Any disagreement was resolved through discussion and consensus among all reviewers Tables 1, 2, and 3.

Description of studies
A total of 1630 records from our initial search in the databases were eligible for title and abstract screening.After removing duplicates (n = 551), 1079 studies were eligible for title and abstract screening.After title and abstract screening, 709 articles were deemed irrelevant and excluded.Then 36 articles were excluded without full texts.After full articles screened, 143 articles were included in the final analysis.The selection process is shown in the PRISMA flow diagram (Fig. 1).
(1) PTSD: Two studies reported the high prevalence of PTSD and symptoms among UN peacekeepers [13,14], ranging from about 5to 20% in a short time after service.Three studies mentioned UN peacekeepers' exposure to stressful events during the missions caused PTSD symptoms after deployment, based on epidemiological study, cross-sectional survey and multi-state models [31,36,37].Notably, one study mentioned that 23 Indian peacekeepers deployed during the study period (2011-2015) reported no PTSD case, which might because that training and experience on counterinsurgency operations and stress busting measures received by Indian soldiers served them well during UN peacekeeping [35].Eight studies mentioned predictors, measures and models for PTSD among peacekeepers such as the Self Rating Inventory for PTSD, to assess the broad range of symptoms and the severity of posttraumatic morbidity [20,23,24,26,28,29,33].Two studies identified a small but significant percentage of peacekeepers with PTSD (8%), and explored the significant association between PTSD symptom severity and increased reports of stressor exposure among U.S. peacekeers in Somalia [21,22].Two studies explored Dutch peacekeepers' PTSD in Cambodia and Yugoslavia through the trauma checklist and MMPI [15,16].One study pointed out the association between PTSD and suicidal ideation (6%) among Norwegian peacekeepers [25].(2) Stress: One study found peacekeepers with higher trait anxiety showed a reduced heart rate increase to the acute psychological stress compared to those with lower trait anxiety [44].Two studies mentioned that UN peacekeepers from an economically poor environment, large families, and a history of unemployment had the high levels of stress due to unfamiliar environment and demanding work [38,39].One study investigated the relationship between stress symptoms and perceived organizational support among 1039 peacekeepers in Kosovo [43], and another study indicated the mechanisms of stress effects on cognitive function and health status among 72 Bulgarian peacekeepers in Kosovo.
One study explored the relationship between the meaningfulness of work, personality hardiness, and their deriving benefits from stressful experiences among U.S. peacekeepers in Bosnia [42].One study explored stress among Pakistani peacekeepers (4%) and highlighted the fact that they were resilient enough to handle the challenges of international environment [45].Another study also explored the incident stress and suggested effective occupational health programs among U.S. peacekeepers [41].(3) Anxiety and depression: One study identified association between combat exposure and mental disorders including anxiety and depression [48].Three studies mentioned the possibility of co-existing      depression and anxiety symptoms in patients with PTSD [20,33,34].Four studies used scales such as Self-Rating Depression Scale and Self-Rating Anxiety Scale to analyze the mental health status of peacekeepers before, during and after deployment, and identified around 6.9% prevalence of depression and around 7.9% prevalence of anxiety [53,58,59,62].Four studies mentioned the use of the Chinese Military Mental Health Scale and the Military Maladaptive Scale to measure Chinese peacekeepers' mental health status, and to find the correlation between their personality characteristics and their mental health levels [50,52,60,61].Six studies used the Symptom Checklist and the Eysenck Personality Questionnaire to evaluate the mental health status of peacekeepers, and found the mental health status of peacekeepers in the medical team was better than those in the transportation team [51,[54][55][56][57]108].(4) Psychiatric disorders: Three studies reported on psychiatric illness and disorders such as panic disorder and substance abuse of UN peacekeepers, associated with suicidal ideation after experiencing frequent panic attacks, among which Australian peacekeepers in Somalia had much higher morbidity than other UN soldiers [13,33,46].
One study investigated 3 cases of HIV/AIDS among Chinese peacekeepers in the Democratic Republic of the Congo [64].Two studies focused on exploring Chinese peacekeepers' knowledge on AIDS, one on the use of knowledge, belief and behavior questionnaire recommended by WHO among 528 peacekeepers in Liberia before and after health education [66], and another on 99.2% (264/266) of peacekeepers' understanding AIDS transmission routes in Sudan [67].(2) Malaria and cholera: Four studies reported the use of chemoprophylaxis agianst cholera and malaria, anti-malarial therapy, screening and vaccination [76][77][78]81].Seven studies reported imported cases and high rates of malaria transmission and intended to characterize the potential causes of malaria outbreak among peacekeepers [70,76,79,80,82,83].Six studies mentioned the care for Chinese peacekeepers against malaria and analyzed the incidence characteristics of malaria and cholera among Chinese peacekeepers [64,[71][72][73][74][75].One study reported a case of falciparum malaria complicated with bronchopneumoniain the Democratic Republic of the Congo [84], and another study researched on malaria and cholera prevention knowledge among Chinese peacekeepers in Sudan [67].(3) Hepatitis E virus (HEV) and Hepatitis A virus (HAV):: Two studies receptively explored Bangladeshi peacekeepers' infection of HEV prior to deployment and determined the prevalence of HEV infection among peacekeepers from the United Nations Mission in Haiti and Haitian civilians [85,86].One study explored a 41-year-old Chinese peacekeeper who manifested fever, jaundice and coagulation dysfunction, and received treatment of severe acute HAV infection in South Sudan [87].(4) Other infectious diseases: Two studies reported dengue fever cases among peacekeepers and outlined measures to prevent local transmission [88,132].One study mentioned the prompt ribavirin treatment of clinically suspected Lassa cases in Sierra Leone [90].One study mentioned the Ebola assessment and care provided in the Chinese Ebola Treatment Unit by Chinese peacekeepers [91].One study identified that Chinese peacekeepers who were repeatedly deployed to high-risk areas of yel-low fever might not be seriously affected by yellow fever virus [89].

Other health problems
Totally  [101,110].One study outlined the dermatological profiles of international peacekeepers in UN second level hospital to retrospectively assess the disease patterns and made comparisons with previous skin disease reports among peacekeepers [104].(3) Leukemia: Two studies mentioned the aroused alert on the exposure to depleted uranium associated with leukemia among European peacekeepers who served in Iraq and the Balkans [102,103].One study compared the post-war cause-specific mortality of 53,320 veterans who deployed to Bosnia/ Kosovo between 1996 and 2002 to that of 117,267 veterans who were not, and found increased risks of disease related mortality among U.S. peacekeepers [111].(4) Others: One study monitored serologic evidence of exposure to diseases that caused acute febrile illness among Mongolian peacekeepers in South Sudan [106].One study was conducted to investigate fatal accidents in Norwegian former peacekeepers, and found the need for preventive measures at reducing the risk of accidental death [93].One study explored peacekeepers' hydration status and cardiac autonomic modulation in Haiti, and found that an operational peacekeeper patrol promoted both dehydration and an imbalance in the autonomic modulation of soldiers' heart rate [117].One study described patterns of homicidal violence among peacekeepers and suggested possible reasons for the attacks [116].
One study explored the increasing proportion of acute acute appendicitis among 462 inpatients in a peacekeeping secondary hospital of Kinshasa from January 2017 to December 2019 [114].One study pointed out the importance of effective surveillance and good microbiology laboratory support towards immunization against rubella during deployments [92].One study reported on ultrasound used in abdominal, superficial, obstetrics and gynecology, and cardiovascular to check peacekeepers' health in the Democratic Republic of the Congo [113].One study demonstrated that the most serious health problems occurring in the group of Polish soldiers in the given period included digestive tract diseases (12.9%) and non-battle injuries (9.2%) [115].One study found conflict exposure was positively correlated with increased risk of mortality from nonneoplastic diseases among Norwegian peacekeepers in Lebanon [105].
Two studies reported the tough and harsh natural environment in host countries, including mold, fungi, and dust, wind, sand, and mountain conditions, which may cause health problems such as heat injuries and low temperature injuries among peacekeepers [62,67,97,118,120].Two studies reported seasonal distribution such as hot climate, sufficient rainfall, dense vegetation as health risk factors of UN peacekeepers in host countries [64,114].One study mentioned most host countries were located in tropical areas, suitable for the survival of many pathogenic bacteria [119].
Seven studies reported peacekeepers' economic conditions and family relationships such as their marriage status are associated with their health status [35,38,39,[121][122][123]150].Ten studies found that previous unemployment, complex war environment, closed camp environment, lack of meaningfulness in stressful mission, inherent work dangers, and differences in culture made peacekeepers actively adapt to social environments, otherwise led to health problems during deployment [17,38,47,49,62,104,110,120,125].Five studies pointed out the importance of social and organizational support, such as providing collective pre-deployment training and improving local health resources, to ensure peacekeepers' health [43,52,64,80,126].Two studies mentioned traffic accidents, munitions and explosives fracture compound injuries among peacekeepers [112,118].One study investigated factors associated with PTSD symptoms, including lower level of education, being single, and more traumatic situations during deployment [124].One study mentioned that peacekeepers' perception of their spouses' support during the deployment had a positive impact on work-to-family enrichment, which mediated their health perception and general satisfaction with life [127].
Four studies mentioned that peacekeepers often suffered from distress because of missing hometown and disharmony in interpersonal relationships, which led to long-term mental fatigue [53,62,104,125].Four studies mentioned peacekeepers' personal barriers to disclose experiences such as traumatic events [15,24,37,42].Three studies suggested peacekeepers to actively cope with mental health distress, have various mental health activities, and build confidence and resilience throughout the deployment [47,49,126].Two studies highlighted peacekeepers' mental health needs and barriers including peacekeepers' feeling of more powerless and threatening, the idea that the mission had become meaningless, and having had no control over the situation [121,124].One study mentioned that when peacekeepers' hardiness were high, their psychological distress became low [128].One study found no association between psychosocial factors (military peace force stressors, clinical stress, anxiety and depression) and blood T lymphocyte among Brazilian peacekeepers in Haiti [129].

Behavioral lifestyle factors
Totally 9 articles reported on behavioral lifestyle factors as health risk factors of UN peacekeepers in multiple troop-contributing and host countries [14,30,52,71,93,104,114,125,131].
Five studies showed peacekeepers' misuse of alcohol and lack of drinking water and having food due to uncertainty during the deployment led to their health problems [14,30,71,93,114].Three studies showed peacekeepers' group living lifestyle with different cultural backgrounds, religious beliefs, and customs require them to improve their adaptability to ensure group work proficiency [52,104,125].One study explored severity PTSD symptoms impacted by exposure to combat directly and indirectly through fear and sexual harassment among U.S. peacekeepers in Somalia [130].One study explored understanding the complex association among peacekeepers' PTSD, coping style, and resilience by focusing on the experiences of Chinese peacekeepers in South Sudan [131].

Biological factors
Totally 3 articles reported on biological factors as health risk factors of UN peacekeepers in multiple troop-contributing and host countries [53,64,110].
Three studies reflected on the causes of infectious disease such as malaria, including poor sanitary conditions and the high prevalence of patients and carriers [53,64,110].

Health service factors
Totally 3 articles reported on health service factors as health risk factors of UN peacekeepers in multiple troopcontributing and host countries [53,64,110].
Two studies mentioned health services included health and disease prevention tasks and the preparation of medical materials such as antimicrobial chemoprophylaxis to avoid infections [64,110].One study mentioned the provision of beneficial mental health care resulted in the improvement of peacekeepers' mentality [53].
Eight studies mentioned the enforcement of preventive medicine such as chemoprophylaxis and antiallergic drugs, immunization, disinfection, screening [67,74,76,78,84,88,92,101].Nine studies emphasized the health education on disease prevention as health protection of UN peacekeepers, such as HIV/AIDS knowledge, malaria chemoprophylaxis and medical examinations [64,66,68,73,79,80,107,114,134].Six studies pointed out the improvement of disease prevention system and policy, including early notification and isolation of cases, diagnosis and management of infectious diseases, malaria protection policy, improved detection systems for mental health problems and individual interventions [65,70,107,132,133,135].
Nine studies mentioned medical and health measures included vaccines, dietary nutrition, hospital treatment such as specialized PTSD treatment and anti-malarial treatment, physiotherapy services, isolation measures, drug preparations [20,72,75,80,87,91,94,95,137].Nine studies pointed out it was important to reinforce coordination with overseas healthcare services, equip specialized professionals and complex equipment, optimize the diet structure, standardize medical surveillance, improve treatment knowledge and plan [79,92,101,107,112,114,136,138,139].One study listed specific examples of a thorough evaluation of severity of subclusters to deal with peacekeepers' health problems [29].Three studies emphasized food hygiene, disinfection of drinking water, and frequent hand washing as medical and health measures for peacekeepers' health protection [64,140,141].
One study explored the impact of a powerful TV drama on the psychological health of U.K. peacekeepers compared with other military personnel [31].Sixteen studies reported psychosocial measures included changing regulations, providing pre-deployment training and guidance, mental health education through lectures and broadcasts, organizational support programs, psychological counseling and intervention [13,14,35,39,43,54,56,82,107,140,142,[144][145][146][147]149].Six studies pointed out there were approaches to stress management and assessment, and peacekeepers were taught to express emotions with teammates and families [29,38,40,44,116,122].Four studies showed the medical standard working and environmental management procedures, to increase peacekeepers' disease awareness and strengthen medical protection [67,80,95,138].Two studies showed the use of psychosocial measures such as the Tachikawa Resilience Scale to know about peacekeepers' coping styles during the deployment [57,148].One study investigated perceived psychological needs and found that they did not require formalised interventions due to already accessing formalised support mechanisms, but additional social support from peers and family were needed among U.K. peacekeepers [143].

Diplomatic measures
Totally 2 articles reported on diplomatic measures as health protection of UN peacekeepers in multiple troopcontributing and host countries [69,83].
One study mentioned the malaria elimination campaigns shared by UN peacekeepers from Sri Lanka, which had malaria eradication since 2012 [83].One study pointed out the incoherent UN policy did not empower the military to exclude HIV positives, which could be seemed as a major factor to find HIV-positive peacekeepers, so better military HIV policies could be used to ensure uniform standards in the teams [69].

Main findings
This scoping review demonstrated that the existing research primarily concentrated on the general health status, health risk factors and health protection of UN peacekeepers in multiple troop-contributing and host countries.Many research explored the health status of UN peacekeepers in Africa deployed from mainly the U.S., Canada, U.K., China, Australia and Norway, and reported mainly on mental health problems and infectious diseases.The current analysis on the health risk factors of UN peacekeepers mainly focused on host countries, and covered natural, social, psychological, behavioral, biological and health service perspectives.The current exploration on health protection of UN peacekeepers was mainly based on previous experience of UN peacekeepers, specifically on disease prevention, medical, psychosocial, and diplomatic measures.However, there was a lack of strategic explorations on complex health risk factors of UN peacekeepers and comprehensive strategies in health protection before, during and after the deployment.
This scoping review found the current research on the health status of UN peacekeepers mainly covered mental health, infectious diseases and a diversity of other diseases.Most peacekeepers suffered from PTSD after deployment [21,26], experienced stress during deployment [41,45], reported anxiety and depression after mental health scale tests [52,61], and a few serious cases experienced psychiatric illness and suicidal ideation [13,33].The majority of articles covered the general mental health status from multination in peacekeeping, with U.S., U.K., Canada, Australia, and China reporting more than other countries on mental health problems among peacekeepers.HIV/AIDS, malaria and cholera were identified and researched by multination including Nigeria, China, Egypt, Sri Lanka, and Bangladesh which sent peacekeepers to Haiti, the Democratic Republic of the Congo, Sudan, Liberia, and South Sudan.Other infectious diseases such as Dengue, Lassa and Yellow fever were identified by a few troop-contributing countries and reported cases for further investigation.Other health problems such as oral, skin, gastrointestinal, musculoskeletal, and respiratory diseases mainly reported by Chinese researchers, according to the diagnosis and treatment report in the Chinese secondary hospitals [104,109,139,151].Leukemia and cancer were explored mainly by countries such as U.S. and Italy, while dehydration and non-battle injuries were explored by countries such as Brazil and Poland [102,103,115,117].
Global health is the study of health problems, health issues, and health concerns across national boundaries, which could influence the health of people through environment and experience of countries around the world [152].Global health problems have cross-border characteristics, whose impact can be transferred to other countries.Our previous research on the Chinese medical team during the Ebola pandemic in Liberia showed that peacekeepers faced the challenges of Ebola as well as other infectious diseases (HIV, malaria, and tuberculosis) and psychological stressors (fear and anxiety) [153].And the COVID-19 outbreak has again posed threats to peacekeepers' health problems and led to severe diseases acorss borders [154].A review by Shigemyra et al. also identified the association between UN peacekeepers' exposure to multiple events and the further development of their health problems after deployment [155].Drabick and Kunkel listed examples of UN Peacekeepers contributing to disease spreading, such as Hepatitis E Infection and the Cholera in Haiti [81,85].The health problems of UN peacekeepers are complicated, and whose impacts are cross-border.
This scoping review found that social environmental factors were explored the most among other health risk factors.Peacekeepers' economic conditions, family relationships, previous employment, war environment, cultural differences, and education level seemed to be social environmental factors associated with their health status, reported by a range of countries such as Norway, U.S., U.K., and China in some peacekeeping areas such as Bosnia, Lebanon and Kosovo [38,62,121,124].A number of troop-contributing countries such as Australia and Netherland also explored psychological factors as health risk factors of UN peacekeepers in host countries such as Lebanon and Haiti.Due to missing hometown, disharmony in interpersonal relationships, and personal barriers to disclose experiences could lead to peacekeepers' psychological distress such as anxiety and depression during and after deployment [49,104,124,129].Natural environmental factors and behavioral lifestyle factors were also seemed to be important health risk factors of UN peacekeepers multiple troop-contributing such as Finland and China, and host countries such as the Democratic Republic of Congo and Somalia.Tough natural environment, hot climate, sufficient rainfall and dense vegetation in host countries may cause health problems such as heat injuries and pathogenic bacteria [97,114,119], while misuse of alcohol, lack of drinking water and food, group living lifestyle, fear and sexual harassment could lead to their health problems during the deployment [14,93,130].Only a small number of articles reported on health service factors and biological factors as health risk factors of UN peacekeepers from China to Mali, Lebanon, and the Democratic Republic of the Congo.Poor sanitary conditions led to infectious disease such as malaria, health and disease prevention services could avoid infections and mental health care could improve peacekeepers' mentality [53,64,110,156].
The health risk factors of UN peacekeepers are complicated and across different countries.Our previous study on the Chinese medical team during the Ebola pandemic in Liberia pointed out that the resource-limited working environment and the underdeveloped local public health system could be health risk factors among UN peacekeepers [153].The limited access to health facilities, the lack of vaccinations, and the insufficient use of personal protective equipment such as facial masks and personal hygiene products could be health risk factors among UN peacekeepers during the COVID-19 pandemic [154].The completion of UN peacekeeping missions required the cooperation between host countries and troop-contributing countries, but this scoping review found that the analysis on the health risk factors of UN peacekeepers was mainly about host countries.Mehlum and Korzeniewski identified different health risk factors among UN peacekeepers, including their tough living conditions and unhealthy lifestyles [14,97].According to the World Health Organization, the Social Determinants of Health (SDH) are the conditions in which people are born, grow, work, live, and age, and the wider set of forces and systems shaping the conditions of their daily life [157].The SDH of UN peacekeepers not only included the health risk factors in host countries, but also involved health risk factors across different countries.
This scoping review found that disease prevention measures, medical and health measures, and psychosocial measures were the main health protection for UN peacekeepers.Psychosocial measures included predeployment training, mental health education, organizational support programs, psychological counseling and intervention, stress management and assessment, and social support from peers and family, to increase peacekeepers' disease awareness and strengthen health protection among peacekeepers from countries such as U.S., U.K., China, Ireland, Bulgaria, etc. who deployed to countries such as Yugoslavia and Liberia [67,80,138,143,158].Disease prevention measures included the enforcement of preventive medicine, the health education on disease prevention, the improvement of disease prevention system and policy reported by troop-contributing countries such as Nigeria and U.K. to host countries such as Bosnia-Herzegovina and South Sudan [65,76,88,107,133].Medical and health measures included reinforcing vaccines, improving hospital treatment, optimizing the diet structure, standardizing medical surveillance, disinfection of drinking water, and frequent hand washing for peacekeepers' health protection from troop-contributing countries such as China and Canada to host countries such as Lebanon and Mali [20,29,79,141].Only Guerra and Assan explored the use of diplomatic measures such as the malaria elimination campaigns and the reinforcement of HIV policy in the UN, to ensure the diplomatic impact on peacekeepers' health protection [69,83].
There are existing programs, policies, regulations, common practices, and rules around the health of UN peacekeepers to prevent the spread of diseases.The Security Council has a peace operation resolution by setting out missions' mandates and monitoring the work of UN peacekeepers through periodic reports [159].The General Assembly monitors the performance of UN Peacekeeping through the Special Committee on Peacekeeping Operations established in 1965, and discusses on matters regarding the health protection of UN peacekeepers through the Uniting for Peace resolution established in 1950 [160].The UN Department of Operational Support has a six-year strategy on operating at minimum risk to UN peacekeepers, troop-contributing and host population, societies and ecosystems, by making on-site risk assessments and promptly implementing health actions [161].The UN Peacekeeping Capability Readiness System aims to establish a dynamic interaction between the UN Headquarters and Member States to strengthen UN peacekeepers' health readiness and timely deployment during the process [162].However, measures demontrsated in this scoping review and existing programs in the UN were taken mainly based on previous experience and lessons, with a lack of theoretical guidance from global health perspectives.

Implications for practice and research
As mentioned above, since health problems of UN peacekeepers are global health issues, health protection of UN peacekeepers could be taken from global health perspectives.Given multiple health risk factors of UN peacekeepers, more formative and implementation research are needed to explore potential strategies on the health protection among peacekeepers.

Multi-phases
The health protection of UN peacekeepers can be divided into three phases.Firstly, before deployment, troopcontributing countries could improve UN peacekeepers' health protection knowledge and take preventive measures such as physical examination, health education, psychological counseling, and vaccination [163,164].Secondly, during the deployment, it is necessary to establish effective health systems that can provide sufficient medical and health services for UN peacekeepers, help them develop healthy life habits, and enhance their health protection skills [138,165,166].Thirdly, after the deployment, it is necessary to pay attention to UN peacekeepers' health conditions and infection risks among wide populations, so it is recommended to take preventive measures for transportation and quarantine when they arrive home [164].

Multi-disciplines
The health protection of UN peacekeepers requires support from multiple disciplines including public health, medicine, politics, health diplomacy, and others.Firstly, public health.The health protection of UN peacekeepers requires insights from the public health discipline to prevent infections in large groups [68,87].Lowicki-Zucca et al. mentioned UN peacekeepers posed public health threats to troop-contributing countries, which need public health experts' solutions and actions on health education and prevention measures [68].Secondly, medicine.Experts from clinical and preventive medicine backgrounds could provide UN peacekeepers with medical treatment [154,167].Lewnard et al. pointed out that screening and vaccination were effective strategies to prevent cholera introduction during large-scale UN peacekeeping deployments such as in the 2010 Haiti outbreak [78], so clinical and preventive medicine are needed in disease prevention and control.Thirdly, politics.Since global health is dedicated to improving health equity for all human beings and integrating health protection into policies, political bodies could cooperate and take political actions such as implementing regulations and laws to protect UN peacekeepers' health [69,154].Despite political actions taken by the UN on HIV transmission among UN peacekeepers, military HIV policies could be facilitated to ensure uniform standards, interpretation, and implementation to guide UN peacekeepers' health behaviors [69].Fourthly, diplomacy.It is critical for governments and organizations to take humanitarian measures in health diplomacy from regional, bilateral, and multilateral perspectives [126,167].Stakeholders involved in UN peacekeeping could take actions to urge political unity, build trust among public institutions, and ensure health equities among UN peacekeepers [167].Fifthly, other disciplines such as logistics management and sociology could be used in their health protection measures [57,154].For instance, the logistic support of medical drugs and equipment could have critical influence on the health protection of UN peacekeepers against parasites and epidemics caused by viruses and bacteria [154].

Multi-levels
The UN peacekeeping is a global mission, which requires global health protection from multi-levels, including the UN, host countries, troop-contributing countries, the UN peacekeeping team, and UN peacekeepers.Firstly, the UN could establish graded treatment institutions and sufficient mechanisms, to ensure health protection and epidemic prevention among peacekeepers.Secondly, host countries and troop-contributing countries could take responsibilities of training peacekeepers [94].Thirdly, UN peacekeeping teams could cooperate and provide health protection for peacekeepers, by including the first-level medical treatment team deployed by most peacekeeping units, and the second-level medical treatment team held by medical professionals from various countries or jointly organized by the surrounding hospitals [109,135].Fourthly, UN peacekeepers themselves could take initiatives of improving health literacy by learning health protection knowledge to ensure the progress of peacekeeping missions [41,109].

Limitations
There are several limitations in this review.Firstly, most measures mentioned in articles of this scoping review were not tested by intervention studies, which could be further practiced and researched.Secondly, we added languages other than English or Chinese as additional filters to search on databases, and found no more articles in other languages on this topic.

Conclusions
This scoping review synthesized current studies on UN peacekeepers' health.This review informed that current research topics on UN peacekeepers' health mainly covered health problems and health risk factors, with a lack of comprehensive health protection measures.UN peacekeepers' health problems are typical global health issues, with complicated and cross-border health risk factors.However, the review showed that the current health protection of UN peacekeepers was mainly based on previous experience of UN peacekeepers.Therefore, more comprehensive strategies could be taken from global health perspectives, including multi-phases, multidisciplines, and multi-levels.The future practice and research on the health of UN peacekeepers is of great significance, in terms of improving the health protection of peacekeepers and consolidating the peacekeeping effectiveness.

Fig. 1
Fig. 1 PRISMA flow chart to show the study selection process.This figure presents the process of selecting research on the health of UN peacekeepers

Table 1
Studies on health status of UN peacekeepers

Table 3
Studies on health protection of UN peacekeepers